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Craig A Grimes - One of the best experts on this subject based on the ideXlab platform.
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self assembled tio2 nanotube arrays by Anodization of titanium in diethylene glycol approach to extended pore widening
Langmuir, 2010Co-Authors: Sorachon Yoriya, Craig A GrimesAbstract:We report on the formation of titanium dioxide nanotube arrays having the largest known pore size, approximately 350 nm diameter. The nanotube arrays are synthesized by Ti foil Anodization in a diethylene glycol electrolyte containing low (0.5−2%) concentrations of hydrofluoric acid. The large pore size nanotube arrays are achieved with extended Anodization durations of approximately 120 h, with the Anodization duration showing a more significant effect on pore diameter than the Anodization voltage. It appears that the combined effects of hydrofluoric acid content and Anodization duration determine the lateral etching rate of the nanotubes, leading to the larger pore size nanotubes.
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synthesis of ordered arrays of discrete partially crystalline titania nanotubes by ti Anodization using diethylene glycol electrolytes
Journal of Materials Chemistry, 2008Co-Authors: Sorachon Yoriya, Sanjeev Sharma, Craig A GrimesAbstract:We report the fabrication of self-organized titania nanotube arrays comprised of separated, discrete nanotubes by Ti Anodization in fluoride ion containing diethylene glycol (DEG) electrolytes. We describe the effect of the fluoride bearing species used in the Anodization electrolyte on the tube morphology, degree of tube-to-tube separation, and crystallization. The arrayed nanotubes achieved from DEG electrolytes containing either HF or NH4F are fully separated with open pores.
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photoelectrochemical and water photoelectrolysis properties of ordered tio2 nanotubes fabricated by ti Anodization in fluoride free hcl electrolytes
Journal of Materials Chemistry, 2008Co-Authors: Nageh K Allam, Karthik Shankar, Craig A GrimesAbstract:Described is the synthesis of TiO2 nanotube array films by Anodization of Ti foil in HCl electrolytes containing different H2O2 concentrations. Highly ordered nanotube arrays up to 860 nm in length, 15 nm inner pore diameter, and 10 nm wall thickness were obtained for one hour Anodizations using a 0.5 M HCl aqueous electrolyte containing 0.1–0.5 M H2O2 concentrations for Anodization potentials between 10–23 V. The use of ethylene glycol as the electrolyte medium significantly alters the Anodization kinetics and resulting film morphologies; nanotube bundles several microns in length achieved for Anodization potentials between 8 V and 18 V in only a few minutes. The nanotube arrays obtained from the ethylene glycol electrolytes show relatively higher photocurrents, ≈0.8 mA cm−2 under AM 1.5. Under 100 mW cm−2 AM 1.5 illumination a 500 °C annealed 1 cm2 nanotube array sample, obtained by Anodization of a Ti foil sample in ethylene glycol + 0.5 M HCl + 0.4 M H2O2 electrolyte, demonstrates a hydrogen evolution rate of approximately 391 μL h−1 by water photoelectrolysis, time-power normalized evolution rate of 3.9 mL W−1 h−1, with water splitting confirmed by the 2 : 1 ratio of evolved hydrogen to oxygen.
Ulrich Gösele - One of the best experts on this subject based on the ideXlab platform.
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self ordered anodic aluminum oxide formed by h2so4 hard Anodization
ACS Nano, 2008Co-Authors: Kathrin Schwirn, Kornelius Nielsch, Martin Steinhart, R Hillebrand, Ulrich GöseleAbstract:The self-ordering of nanoporous anodic aluminum oxide (AAO) in the course of the hard Anodization (HA) of aluminum in sulfuric acid (H2SO4) solutions at Anodization voltages ranging from 27 to 80 V was investigated. Direct H2SO4-HA yielded AAOs with hexagonal pore arrays having interpore distances Dint ranging from 72 to 145 nm. However, the AAOs were mechanically unstable and cracks formed along the cell boundaries. Therefore, we modified the Anodization procedure previously employed for oxalic acid HA (H2C2O4-HA) to suppress the development of cracks and to fabricate mechanically robust AAO films with Dint values ranging from 78 to 114 nm. Image analyses based on scanning electron micrographs revealed that at a given Anodization voltage the self-ordering of nanopores as well as Dint depend on the current density (i.e., the electric field strength at the bottoms of the pores). Moreover, periodic oscillations of the pore diameter formed at Anodization voltages in the range from 27 to 32 V, which are remin...
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Structural engineering of nanoporous anodic aluminium oxide by pulse Anodization of aluminium.
Nature nanotechnology, 2008Co-Authors: Woo K. Lee, Ulrich Goesele, Woo Lee, Eckhard Pippel, Kathrin Schwirn, Martin Steinhart, Roland Scholz, Ulrich GöseleAbstract:Nanoporous anodic aluminium oxide has traditionally been made in one of two ways: mild Anodization or hard Anodization. The first method produces self-ordered pore structures, but it is slow and only works for a narrow range of processing conditions; the second method, which is widely used in the aluminium industry, is faster, but it produces films with disordered pore structures. Here we report a novel approach termed "pulse Anodization" that combines the advantages of the mild and hard Anodization processes. By designing the pulse sequences it is possible to control both the composition and pore structure of the anodic aluminium oxide films while maintaining high throughput. We use pulse Anodization to delaminate a single as-prepared anodic film into a stack of well-defined nanoporous alumina membrane sheets, and also to fabricate novel three-dimensional nanostructures.
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self ordering behavior of nanoporous anodic aluminum oxide aao in malonic acid Anodization
Nanotechnology, 2007Co-Authors: Woo Lee, Kornelius Nielsch, Ulrich GöseleAbstract:The self-ordering behavior of anodic aluminum oxide (AAO) has been investigated for Anodization of aluminum in malonic acid (H4C3O4) solution. In the present study it is found that a porous oxide layer formed on the surface of aluminum can effectively suppress catastrophic local events (such as breakdown of the oxide film and plastic deformation of the aluminum substrate), and enables stable fast anodic oxidation under a high electric field of 110‐140 V and ∼100 mA cm −2 . Studies on the self-ordering behavior of AAO indicated that the cell homogeneity of AAO increases dramatically as the Anodization voltage gets higher than 120 V. Highly ordered AAO with a hexagonal arrangement of the nanopores could be obtained in a voltage range 125‐140 V. The current density (i.e., the electric field strength (E) at the bottom of a pore) is an important parameter governing the self-ordering of the nanopores as well as the interpore distance (Dint) for a given Anodization potential (U ) during malonic acid Anodization. S Supplementary data are available from stacks.iop.org/Nano/18/475713 (Some figures in this article are in colour only in the electronic version)
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Fast fabrication of long-range ordered porous alumina membranes by hard Anodization.
Nature materials, 2006Co-Authors: Woo K. Lee, Ulrich Goesele, Woo Lee, Ulrich Gösele, R Ji, Kornelius NielschAbstract:Nanoporous anodic aluminium oxide has been widely used for the development of various functional nanostructures. So far these self-organized pore structures could only be prepared within narrow processing conditions. Here we report a new oxalic-acid-based Anodization process for long-range ordered alumina membranes. This process is a new generation of the so-called "hard Anodization" approach that has been widely used in industry for high-speed fabrication of mechanically robust, very thick (>100 microm) and low-porosity alumina films since the 1960s. This hard Anodization approach establishes a new self-ordering regime with interpore distances, (D(int))=200-300 nm, which have not been achieved by mild Anodization processes so far. It offers substantial advantages over conventional Anodization processes in terms of processing time, allowing 2,500-3,500% faster oxide growth with improved ordering of the nanopores. Perfectly ordered alumina membranes with high aspect ratios (>1,000) of uniform nanopores with periodically modulated diameters have been realized.
Kourosh Kalantarzadeh - One of the best experts on this subject based on the ideXlab platform.
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Anodization of ti thin film deposited on ito
Langmuir, 2009Co-Authors: A Z Sadek, Haidong Zheng, Kay Latham, W Wlodarski, Kourosh KalantarzadehAbstract:We have investigated several key aspects for the self-organization of nanotubes in RF sputtered titanium (Ti) thin films formed by the Anodization process in fluoride-ion-containing neutral electrolytes. Ti films were deposited on indium tin oxide (ITO) glass substrates at room temperature and 300 °C, and then anodized. The films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV−vis spectrometry before and after Anodization. It was observed that Anodization of high temperature deposited films resulted in nanotube type structures with diameters in the range of 10−45 nm for an applied voltage of 5−20 V. In addition, the anatase form of TiO2 is formed during the Anodization process which is also confirmed using photocurrent measurements. However, the Anodization of room temperature deposited Ti films resulted in irregular pores or holes.
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fabrication of nanostructured tio2 by Anodization a comparison between electrolytes and substrates
Sensors and Actuators B-chemical, 2008Co-Authors: W Wlodarski, Sasikaran Kandasamy, Kourosh KalantarzadehAbstract:Nanostructured TiO2 thin films with large surface to volume ratio are fabricated from titanium thin films deposited on various substrates employing an Anodization technique. The effect of the electrolytes (e.g. HF-containing electrolyte or neutral electrolyte) and substrates (e.g. silicon substrate or silicon carbide substrate) on the microstructure of the anodized thin films are investigated. Nanoporous films on silicon substrates with an average pore diameter of 25 nm and interpore distance of 40 nm are obtained by anodizing in an aqueous HF electrolyte solution after a comprehensive investigation of the Anodization conditions. When the Anodization is performed in a neutral electrolyte without HF solution, discrete nanotubular thin films are formed. The anodic film on silicon carbide substrate shows a quite different morphology, which exhibits a layered structure after Anodization. The nanostructured TiO2 films are characterized using SEM and XRD techniques and their formation conditions are discussed. In addition, a growth mechanism model is presented to explain the formation of different nanostructures.
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formation of nanoporous titanium oxide films on silicon substrates using an Anodization process
Nanotechnology, 2006Co-Authors: Qunbao Yang, Nanfei Zhu, Kourosh KalantarzadehAbstract:The formation of nanoporous TiO2 by Anodization of titanium films deposited on silicon substrates was investigated. Films with homogeneously distributed pores having an average pore diameter of 25 nm and interpore distance of 40 nm were obtained by Anodization in an aqueous HF electrolyte solution after a comprehensive investigation of the Anodization conditions. It was shown that the magnitude of the Anodization current and voltage have significant roles in the formation of different surface morphologies with different pore dimensions, ranging from big pits to nanosize porous structures. The study showed that the nanoporous structure is formed only in 0.5–1.0 wt% HF solution while keeping the anodizing potential at 3–5 V. The porous TiO2 films were characterized using scanning electron microscopy and x-ray diffraction techniques, and their formation conditions are discussed. In addition, a growth mechanism model is presented to explain the formation of different surface structures.
Dusan Losic - One of the best experts on this subject based on the ideXlab platform.
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Structural Engineering of Nanoporous Anodic Alumina Photonic Crystals by Sawtooth-like Pulse Anodization
ACS Applied Materials & Interfaces, 2016Co-Authors: Cheryl Suwen Law, Abel Santos, Mahdieh Nemati, Dusan LosicAbstract:This study presents a sawtooth-like pulse Anodization approach aiming to create a new type of photonic crystal structure based on nanoporous anodic alumina. This nanofabrication approach enables the engineering of the effective medium of nanoporous anodic alumina in a sawtooth-like manner with precision. The manipulation of various Anodization parameters such as Anodization period, Anodization amplitude, number of Anodization pulses, ramp ratio and pore widening time allows a precise control and fine-tuning of the optical properties (i.e., characteristic transmission peaks and interferometric colors) exhibited by nanoporous anodic alumina photonic crystals (NAA-PCs). The effect of these Anodization parameters on the photonic properties of NAA-PCs is systematically evaluated for the establishment of a fabrication methodology toward NAA-PCs with tunable optical properties. The effective medium of the resulting NAA-PCs is demonstrated to be optimal for the development of optical sensing platforms in combinat...
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optimizing Anodization conditions for the growth of titania nanotubes on curved surfaces
Journal of Physical Chemistry C, 2015Co-Authors: Karan Gulati, Abel Santos, David M Findlay, Dusan LosicAbstract:Titania nanotubes (TNTs), fabricated by electrochemical Anodization due to their outstanding properties, have been widely explored for solar cells, catalysis, electronics, drug delivery, biosensing, and medical implants. Rational design of the Anodization conditions is the key to obtaining high quality TNTs that are well aligned and strongly adherent onto the underlying titanium substrate. With the development of many Anodization procedures on a substrate with various shapes and sizes, catering to various applications, the mechanical stability of anodic layers is often neglected. Here we consider the factors that lead to unstable and poorly adherent nanotube arrays produced upon Anodization of curved titanium surfaces. The role of electrolyte aging, water content, voltage/time of Anodization, and the substrate dimensions were investigated for optimization of the fabrication of nanotubes on curved surfaces such as Ti wires. Finally, the most optimal fabrication procedure and Anodization parameters are pres...
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nanopore gradients on porous aluminum oxide generated by nonuniform Anodization of aluminum
ACS Applied Materials & Interfaces, 2010Co-Authors: Krishna Kant, Suet P Low, Asif Marshal, Joseph G Shapter, Dusan LosicAbstract:A method for surface engineering of structural gradients with nanopore topography using the self-ordering process based on electrochemical Anodization of aluminum is described. A distinct Anodization condition with an asymmetrically distributed electric field at the electrolyte/aluminum interface is created by nonparallel arrangement between electrodes (tilted by 45°) in an electrochemical cell. The anodic aluminum oxide (AAO) porous surfaces with ordered nanopore structures with gradual and continuous change of pore diameters from 80 to 300 nm across an area of 0.5−1 cm were fabricated by this Anodization using two common electrolytes, oxalic acid (0.3 M) and phosphoric acid (0.3 M). The formation of pore gradients of AAO is explained by asymmetric and gradual distribution of the current density and temperature variation generated on the surface of Al during the Anodization process. Optical and wetting gradients of prepared pore structures were confirmed by reflective interferometric spectroscopy and con...
Jinsub Choi - One of the best experts on this subject based on the ideXlab platform.
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Porous niobium oxide films prepared by Anodization annealing Anodization
Nanotechnology, 2007Co-Authors: Jinsub ChoiAbstract:In this paper, a method to prepare anodic porous niobium oxide with a thickness of more than half a micrometre is described in terms of delaying the chemical dissolution of the formed oxide in fluorinated electrolytes either by controlling the Anodization temperature or by making a protective oxide. It was revealed that both the growth rate and the dissolution rate in the formation of porous niobium oxide films increase as the Anodization temperature increases. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) analyses show that the anodically prepared niobium oxide consists of amorphous Nb2O5. For the strategy to make protective oxide, self-ordered nanoporous niobium oxide with double layers consisting of an outer layer of around 90–130 nm and an inner layer of around 300–400 nm is prepared by Anodization–annealing–Anodization. We believe that the outer oxide, which undergoes annealing, plays the role of a protective layer for the formation of the inner oxide film grown underneath the outer layer, leading to anodic niobium oxide with a thickness greater than that obtained by single Anodization.
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porous niobium oxide films prepared by Anodization in hf h3po4
Electrochimica Acta, 2006Co-Authors: Jinsub Choi, Jae Hoon Lim, Sang Cheon Lee, Jeong Ho Chang, Kyung Ja Kim, Min Ae ChoAbstract:Abstract Ordered porous niobium oxide with the diameter of less than 10 nm and the aspect ratio of more than 20 is prepared by Anodization of niobium foils at 2.5 V in the mixture of 1 wt% HF and 1 M H 3 PO 4 for 1 h. In this study, the effects of the mixed electrolytes, anodic potential and Anodization time on the preparation of porous niobium oxide are described based on the current–time transients during Anodization and morphological observations. It is founded that a single HF electrolyte leads to the formation of pores as well as the fast dissolution of formed pores at the surface. The dissolution of the formed oxide is significantly retarded by the addition of appropriate amount of H 3 PO 4 .
